2005-06-17

Naming things, or, Plan ahea

The naming of stars is a difficult matter, not one of your everyday holiday games. The sky is divided into 88 arbitrary areas of varying size called constellations, and ordinary stars are named in order of brightness by a Greek letter followed by the name of the constellation (in Latin, traditionally in the genitive case). Thus Alpha Centauri is the brightest star in the constellation of the Centaur, and Tau Ceti is the 19th brightest star in the constellation of the Whale. This system is fairly simple and rational, since stars are naturally going to be discovered in order from brightest to dimmest, as telescopes become more powerful.

(From the 25th brightest star on, numbers (which are assigned by location in the sky, not by brightness) are used, and for obscure stars, numbers in star catalogues.)

Stars which are, for any reason, of variable brightness don't fit neatly into the rank order. If the star already had an ordinary name before its variability was noticed, it keeps it. Otherwise, variable stars are given Latin-letter names in order of discovery, followed again by the name of the constellation, thus: R, S, T, U, V, W, X, Y, Z. S Doradus, for example, one of the most luminous (and bizarre) stars known, is the second variable star discovered in the constellation of the Dolphin. (The reason for beginning with R is to avoid colliding with the letters designating spectral types, which are O, B, A, F, G, K, M — but that's a story for another day.) All was well.

But some constellations were found to contain more than nine variable stars.

But some constellations were found to contain more than 90 variable stars.

No problem: astronomers wrapped around the Latin alphabet, thus: AA, AB, ... AZ, ..., BA, ... QZ, omitting the letter J (most of this system was invented in Germany, which was still on Fraktur at the time). All was well.

But some constellations were found to contain more than 334 variable stars.

Two-letter sequences beginning with R-Z had already been been used at an earlier stage, so RA, ... RQ, SA, ..., SQ, ... ZQ were rejected. Instead the final stage of nomenclature became (at very long last) V335, V336, .... Which could and should have been done in the first place instead of the fourth place.

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